Don’t judge cooked meat by its color.

Just… don’t.

Everyone, myself included, does it. We look at the color of the inside of a burger or chicken to determine if it’s cooked. Is it pink? Nope. Chomp chomp!

Here’s the problem: Color is not a good indicator of safe cooking temperatures. You have to use a meat thermometer to be sure meat is cooked to safe temperatures.

Meat turns from pink to brown because the protein that makes meat red (myoglobin) is denatured as it is cooked. The protein is damaged and doesn’t reflect light in the same manner anymore, so the meat appears brown.

Lots of factors can affect how quickly or slowly the protein is denatured as it is heated. Meat color changes can vary due to the pH (acidity) of the meat, the age and gender of the animal, how long it was stored, the way it was packaged, whether it was frozen, even the feed and water of the animals can affect cooked meat color.

Sometimes meat turns brown too soon!

Meat scientists call this phenomenon Premature Browning. It can be really dangerous because meat looks done, but it hasn't been cooked to a safe temperature.

This photo is from a great fact sheet about beef color from the National Cattlemen’s Beef Association. Both of these patties were cooked to an unsafe temperature (55°C or 131°F). Patty A looks very undercooked, but patty B looks done.

I have a previous blog post about fresh meat color. Remember that we talked about meat being oxygenated (red), deoxygenated (purple), or oxidized (brown)? Researchers at Kansas State found that when patties were cooked in the oxidized (brown) state, their cooked color was brown, even at temperatures that were too low to kill deadly bacteria like E. coliand Salmonella. Other research has found that the packaging can cause meat to brown faster, too.

Regardless of why the meat turns brown at too low of a temperature, sometimes it happens. The best way to insure that your meat is cooked properly is to use a meat thermometer.

Ground beef should be cooked to 160°F and poultry should be cooked to 165°F.

Sometimes meat stays pink too long!

Meat scientists call this phenomenon Persistent Pinking. It is not as much a food safety issue as it is a perception and eating quality issue. When meat looks pink, even if it’s been thoroughly cooked, people will think it’s undercooked and will keep cooking it until its way overcooked. When it’s overcooked, it tastes terrible.

I am conducting research on persistent pinking in ground beef this summer. 

These patties were all cooked to exactly 160°F.
You can see how some of them are still pink in the middle.

Research has shown that a high pH (more basic) can protect the proteins at greater temperatures and keep them from turning brown. They may also stay pink because of a higher concentration of the myoglobin protein. Right now our research is creating more questions than answers, but it sure is interesting.

Persistent pinking can also be caused by outside substances interacting with the meat and creating the pink color.

Nitrites are a good example of one of these outside substances. Sometimes we want this pink color to appear, like in the case of ham, sausages, or bacon. However, very small amounts of nitrites can get into the meat (especially poultry) and create a pink color that kind of looks like ham. If you don’t expect the meat to be pink and it is, you may think it’s undercooked.

These pictures were sent to me by Dr. Jim Claus at the University of Wisconsin. He is one of the leading researchers in persistent pinking in processed meats. These are a pair of turkey slices and some tuna chunks with persistent pinking problems. All of these were cooked to a safe temperature, but some clearly have some color issues.

This is a pork chop that was cooked wrapped in bacon. Looks like the nitrites in the bacon seeped into the pork chop and created a pink color.

Sometimes the ovens that cook the meat can introduce gasses that react with the muscle and cause it to turn pink. We like it when this happens in smoked meats, but when you don’t expect it, you may be concerned it hasn’t been cooked enough.

This is a smoked sausage from an awesome BBQ restaurant in south Texas. See how the smoke has created the ring of pink around the edge of the sausage?

When you see pink color in meat, look to see where the off-color is within the pieces. Undercooked meat will be pink in the middle, but persistent pinking issues are more likely to occur on the surface.

Even what the animals (especially birds) eat or drink can introduce substances that can change the cooked color of their meat. Nitrates and nitrites that occur naturally in the feed and water can remain in the birds and create some color problems, especially around the bone.

This is another picture of some cooked chicken pieces from Dr. Claus. You can see some really severe pinking problems in them.

If you are served something that you think looks underdone, it’s OK to ask what temperature it was cooked to. Sometimes meat is just stubbornly pink, but sometimes it may actually be underdone. When it comes to my kids, if I think a piece of meat they've been served may be underdone, you bet I'll ask the waiter about it. 

The best way to know is to use a meat thermometer.

Cook it to a temperaturenot a color.

The USDA has a great fact sheet about meat color that gives more detail about persistent pinking and premature browning.

reade more... Résuméabuiyad

Meat color is a-changin’!

Let’s say you bought some steaks or a roast at the grocery store, brought it home and stuck it in the fridge. (Hopefully, stored on a plate on the bottom shelf.) You don’t get around to fixing it (that’s Texan for preparing it) for supper for a day or two. You take it out of the fridge and it has a brownish color. Maybe a few brown spots or maybe the whole thing is just a little browner than it was when you bought it. Has it gone bad? Should you throw it out? It wasn’t cheap, so you hate to throw it out. What to do?

Check the use-by date. Smell it. Does it smell bad? If it doesn’t smell bad and if you haven’t passed the use-by date, it’s probably ok.

Why is it brown in my fridge when it was red in the store?
 

Short answer. It oxidized. Muscle has an ability to prevent (really slow down) oxidation, but that ability runs out with time. Oxidized muscle is brown.

Long answer. Well, to understand why meat is brown, we need to understand why it was red, first.

Meat contains lots of proteins. Some are structural (they hold the meat together). Some are for contraction (remember that the meat was originally for moving an animal around). Some proteins hold onto oxygen to help provide the muscle with energy.

These oxygen-holding proteins are largely responsible for meat color. The main one is called myoglobin. Myoglobin is closely related to the hemoglobin that holds oxygen as it is transported through our blood. Just like we learned in sixth grade science class that blood comes in two colors (red when it is exposed to oxygen in the arteries and blue when the oxygen is gone in the veins), meat pigment comes in those two colors, too. When it is not exposed to oxygen, meat has a purple color. You can see this color right after it is cut. Meat scientists call this ‘deoxymyoglobin’ because the myoglobin doesn’t have any oxygen. If you buy meat that has been vacuum packaged, it will be purplish in color.

The meat will slowly take up oxygen from the air and turn red. In the meat business, we refer to the time it takes go from purple to red as ‘bloom time’. Most of the meat you buy in the store has been packaged so that the oxygen in the air is available to combine with the myoglobin in the meat. That’s why it is a pretty red color in the store.

We recently did a research project studying bloom time. This is a picture of some steaks from that study. The ones in the front had just been removed from a vacuum package and were the purplish deoxymyoglobin. The ones in the back had been setting out for an hour, and you can see the bright red color.

Purple to red… what about brown?

Ok. So, even though the animal is no longer living, the enzymes in the muscle are still somewhat functional. The enzymes in charge of using oxygen to produce energy will take the oxygen and metabolize it. To do this, the pigment (actually, the iron in the pigment) is oxidized (it loses electrons). When the iron is oxidized, the meat will turn brown.

 In fresh meat, other enzymes can fix the problem by reducing the iron (give it electrons back) and it will turn back to purple. Then, it can grab some more oxygen and produce more energy and the cycle begins again. This really only happens on the surface of the meat where it is exposed to oxygen, so at first, you have a red layer with the purple underneath (everywhere on the meat that is exposed to air will be red. You won’t see the purple unless you cut it). At first, the brown coloring is not around long enough to see. As the process slows with time, a brown layer of pigment will form between the red and purple.

Eventually, the enzymes will run out completely and the muscle will not be able to fix the oxidized, brown pigment and it will turn completely brown on the surface. That is the brown coloring you see. If you leave it long enough, the oxidation could spread to the fat and cause some off-flavors, but the paying attention to the use-by date should prevent that.

Here is a picture from a study we conducted. Some steaks were left in retail cases (in our lab) for a week and allowed to turn brown. Then we cut them into little cubes. You can see the completely oxidized brown coloring on the surface and the purple coloring in the middle.

Just remember to pay attention to the use-by dates on the package and if you don’t cook it by then, freeze it by then.  Use your nose and feel if the meat is slimy. If it’s smelly or slimy, cut your losses and throw it out.

I also have a video blog about why meat is red.

reade more... Résuméabuiyad